Method and apparatus for hashing over multiple frequency bands in a communication system

ABSTRACT

Method and apparatus for hashing mobile stations to frequencies in a communication system. The method uses two-level hashing to assign a mobile station first to frequency band and then to a specific frequency within the frequency band. Embodiments allow for weights to be assigned to frequencies and mobiles hashed to the weighted frequencies. Weighting allows for a non-uniform distribution of mobile stations among frequencies to optimize system operating parameters.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent claims priority of U.S. ProvisionalApplication No. 60/658,049, filed Mar. 2, 2005, assigned to the assigneehereof and hereby expressly incorporated by reference herein.

BACKGROUND

1. Field

The present invention pertains generally to communications, and morespecifically to a novel and improved method and apparatus for hashingover multiple frequency bands in a communication system.

2. Background

Communication systems and wireless systems in particular, are designedwith the objective of efficient allocation of resources among a varietyof users. Wireless system designers in particular aim to providesufficient resources to satisfy the communication needs of itssubscribers while minimizing costs. Efficient use of resources requiresprompt assignment of mobile stations to specific frequencies.

In a wireless communication system employing a Code Division-MultipleAccess (CDMA) scheme or Wideband Code Division Multiple Access (WCDMA)each of the subscriber units is assigned code channels at designatedtime intervals on a time multiplexed basis. A central communicationnode, such as a Base Station (BS) or Node B, implements the uniquecarrier frequency or channel code associated with the subscriber toenable exclusive communication with the subscriber. Time DivisionMultiple Access (TDMA) schemes may also be implemented in landlinesystems using physical contact relay switching or packet switching. ACDMA system may be designed to support one or more standards such as:(1) the “TIA/EIA/IS-95-B Mobile Station-Base Station CompatibilityStandard for Dual-Mode Wideband Spread Spectrum Cellular System”referred to herein as the IS-95 standard; (2) the standard offered by aconsortium named “3rd Generation Partnership Project” referred to hereinas 3GPP; and embodied in a set of documents including Document Nos. 3GTS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214, 3G TS 25.302,referred to herein as the W-CDMA standard; (3) the standard offered by aconsortium named “3rd Generation Partnership Project 2” referred toherein as 3GPP2, and TR-45.5 referred to herein as the cdma2000standard, formerly called IS-2000 MC, or (4) some other wirelessstandard.

CDMA2000 is an improvement on TIA/EIA-95. It provides a significantimprovement in voice capacity and extended data capability and isbackward compatible with TIA/EIA-95 mobiles. When a mobile station movesbetween base stations in a CDMA2000 system the mobiles must register andbe assigned a frequency for communication. The frequency assignmentoccurs during a registration process. Registration includes a hashingprocess to assign a frequency to the mobile station. The mobile mustre-register when changing between base stations, with each changeforcing a new hash to a new frequency, and in many cases a new frequencyband. Hashing is triggered for any change in the frequency distributionor frequency weights. Frequency distribution and weighting is animportant consideration for balancing system loading and ensuringefficient system operation. The mobile station also updates the systemoverhead information each time a hash is performed. This can result inadditional and excessive frequency changes, as every frequency changeresults in system acquisition and reading system overhead information.Unfortunately, while re-acquiring the system pages messages directed tothe mobile station may be missed.

Accordingly, there is a need for a method and apparatus for hashingmobiles over multiple bands while avoiding unnecessary frequencychanges.

SUMMARY

Embodiments disclosed herein address the above stated needs by providinga means for hashing mobiles over multiple frequency bands. Oneembodiment provides method comprising hashing a mobile station to afrequency band; and then hashing the mobile station to a specificfrequency within that frequency band. In another embodiment, A methodcomprising:

-   -   hashing a mobile station to a frequency band using inter-band        hashing, wherein the inter-band hashing is based on a message.

In another embodiment, a method for interband hashing is provided. Themethod first hashes a mobile station to a frequency band using interbandhashing. The interband hashing is based on a message from the basestation.

A still further embodiment provides a method for hashing a mobilestation to a particular frequency by sending a message from a firstdevice to a second device, receiving the information in the firstdevice, and then hashing the first device to a frequency band based onthe information in the message.

An additional embodiment provides for weight-based hashing. Weight-basedhashing may result in a non-uniform distribution of mobile stationsamong the supported frequencies. Each frequency within a frequency bandis assigned a weight. The mobile stations are then hashed tofrequencies, with the heavier weighted frequencies being assigned moremobile stations than lighter weighted frequencies.

Weight-based hashing may also be used with more than one frequency band.In this case, each frequency within each frequency band may be assigneda weight. Mobile stations receive a message containing a list offrequency bands with the weights assigned to frequencies within thosefrequency bands. The mobile station is hashed to a frequency band and toa specific frequency within that band based on the assigned weights.

Yet another embodiment provides for computer instructions for hashing amobile station to a frequency band and then hashing the mobile stationto a specific frequency within the frequency band.

A still further embodiment provides computer instructions for sending amessage from a first device to a second device, receiving information inthe message at the first device, and hashing the first device to afrequency band based on the information in the message.

A further embodiment provides computer instructions for assigningweights to each frequency within a frequency band, hashing a mobilestation to a frequency based on the weight assigned by the computerinstructions to that frequency, and distributing mobile stations acrossfrequencies based on the weights assigned to the frequencies. This mayresult in a non-uniform distribution of mobile stations across thedifferent frequencies.

Another embodiment provides computer instructions for assigning weightsto each frequency within more than one frequency band, sending a messageto a mobile station containing a list of frequency bands and a list offrequencies within those frequency bands. Each frequency within afrequency band has an assigned weight. The mobile station reviews thelist of frequency bands and frequencies and eliminates those frequenciesit is not equipped to support. The mobile sorts the bands andfrequencies in order to have a stable hashing process across basestations. The mobile is then hashed to a frequency band and then hashedto a frequency within that frequency band, based on the computerinstructions.

One embodiment provides a network comprising: means for hashing a mobilestation to a frequency band; means for determining frequency bandassignments for each mobile station; means for hashing the mobilestation to a specific frequency within the frequency band; and means forrepeating the hashing process for each mobile station in the network.

Another embodiment provides an apparatus that includes: means forhashing a mobile station to a frequency band; and means for hashing themobile station to a specific frequency within the frequency band.

A further embodiment provides an apparatus that includes means forhashing a mobile station to a frequency band using inter-band hashing.In this embodiment, the inter-band hashing is carried out based on amessage.

An additional embodiment provides an apparatus for multiple band hashingusing assigned frequency weights. The apparatus includes means forassigning a weight to each frequency within each frequency band, meansfor assigning a weight to a band based on weights of frequencies withinthat band, means for sending a message to a mobile station containing alist of frequency bands as well as a list of frequencies within thosefrequency bands. Each individual frequency is assigned a weight and thisinformation is sent to the mobile station in a message. Additional meansis also provided for the mobile station to review the frequency bandsand frequencies within those bands. The mobile contains means foreliminating frequencies it does not support. The mobile contains meansfor sorting the bands and frequencies in order to have a stable hashingprocess across base stations. The apparatus also includes means forhashing a mobile station to a frequency band and means for hashing amobile station to a frequency within the frequency band, based on theassigned weights.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the presently disclosed methodand apparatus will become more apparent from the detailed descriptionset forth below when taken in conjunction with the drawings in whichlike reference characters identify correspondingly throughout andwherein:

FIG. 1 is a wireless communication system according to an embodiment ofthe invention.

FIG. 2 is a call scheduling overview diagram.

FIG. 3 is a wireless communication system supporting hashing overmultiple bands while avoiding unnecessary frequency changes.

FIG. 4 illustrates the fields and field lengths of the synchronizationchannel message.

FIG. 5 illustrates the method of hashing used on the forward pagingchannel (FPCH).

FIG. 6 details the structure of the registration message.

FIG. 7 shows the fields and field lengths for the request order.

FIG. 8 shows the fields and field lengths for parameter changenon-autonomous registration.

FIG. 9 shows the fields and field lengths for the origination message.

FIG. 10 shows the fields and field lengths for the system parametersmessage.

FIG. 11 shows weight-based hashing coupled with a two-level hashinglogic 1/2.

FIG. 12 is a flowchart of weight-based hashing coupled with a two levelhashing logic, 2/2.

FIG. 13 shows sorting frequencies within a frequency band prior tohashing.

DETAILED DESCRIPTION OF THE INVENTION

A modern day communication system is desired to support a variety ofapplications. One such communication system is a code division multipleaccess (CDMA) system which conforms to the “TIA/EIA-95 MobileStation-Base Station Compatibility Standard for Dual-Mode WidebandSpread Spectrum Cellular System” and its progeny, hereinafter referredto as IS-95. The CDMA system allows for voice and data communicationsbetween users over a terrestrial link. An updated version of a CDMAsystem is known as CDMA2000. The use of CDMA techniques in a multipleaccess communication system is disclosed in U.S. Pat. No. 4,901,307,entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USINGSATELLITE OR TERRESTRIAL REPEATERS”, and U.S. Pat. No. 5,103,459,entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULARTELEPHONE SYSTEM”, both assigned to the assignee of the presentinvention and incorporated by reference herein.

Aspects of the invention are disclosed in the following description andrelated drawings directed to specific embodiments of the invention.Alternate embodiments may be devised without departing from the scope ofthe invention. Additionally, well-known elements of the invention willnot be described in detail or will be omitted so as not to obscure therelevant details of the invention.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration”. Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Likewise, the term “embodiments ofthe invention” does not require that all embodiments of the inventioninclude the discussed feature, advantage, or mode of operation.

In a CDMA system or CDMA2000 system, communications between users areconducted through one or more base stations. In wireless communicationsystems, forward link refers to the channel through which signals travelfrom a base station to a subscriber station, and reverse link refers tothe channel through which signals travel from a subscriber station to abase station. By transmitting data on a reverse link to a base station,a first user on one subscriber station communicates with a second useron a second subscriber station. The base station receives the data fromthe first subscriber station and routes the data to a base stationserving the second subscriber station. Depending on the location of thesubscriber stations, both may be served by a single base station ormultiple base stations. In any case, the base station serving the secondsubscriber station sends the data on the forward link. Instead ofcommunicating with a second subscriber station, a subscriber station mayalso communicate with a terrestrial network (e.g., Internet) through aconnection with a serving base station. In wireless communications suchas those conforming to IS-95, forward link and reverse link signals aretransmitted within disjoint frequency bands.

The telephone system is composed of two segments: the wired subsystemand the wireless subsystem. The wired system is the Public SwitchedTelephone Network (PSTN) and the Internet. It may also includeinstrumentation, video or other services. The wireless subsystemincludes the Base Station subsystem, which involves the Mobile SwitchingCenter (MSC), the Base Station Controller (BSC), the Home LocationRegister (HLR), the Visitor Location Register (VLR), the BaseTransceiver Station (BTS), and the Mobile Station (MS).

FIG. 1 serves as an example of a communications system 100 that supportsa number of users and is capable of implementing at least some aspectsand embodiments presented herein. System 100 provides communication fora number of cells 102A through 102G, each of which is serviced by acorresponding base station (BS) 104A through 104G, respectively. In theexemplary embodiment, some of base stations 104 have multiple receiveantennas and others have only one receive antenna. Similarly, some ofbase stations 104 have multiple transmit antennas, and others havesingle transmit antennas. There are no restrictions on the combinationsof transmit antennas and receive antennas. Therefore, it is possible fora base station 104 to have multiple transmit antennas and a singlereceive antenna, or to have multiple receive antennas and a singletransmit antenna, or to have both single and multiple transmit andreceive antennas.

Mobile Stations (MSs) 106 in the coverage area may be fixed (i.e.,stationary) or mobile. As shown in FIG. 1, various MSs 106 are dispersedthroughout the system. Each terminal 106 communicates with at least oneand possibly more base stations 104 on the downlink and uplink at anygiven moment depending on, for example, whether soft handoff is employedor whether the terminal is designed and operated to (concurrently orsequentially) receive multiple transmissions from multiple basestations. Soft handoff in CDMA communications systems is well known inthe art and is described in detail in U.S. Pat. No. 5,101,501, entitled“Method and system for providing a Soft Handoff in a CDMA CellularTelephone System”, which is assigned to the assignee of the presentinvention and is incorporated by reference in its entirety.

The downlink refers to transmission from the BS to the MS, and theuplink refers to transmission from the MS to the BS. In the exemplaryembodiment, some of MSs 106 have multiple receive antennas and othershave only one receive antenna. In FIG. 1, BS 104A transmits data to MSs106A and 106J on the downlink, BS 104B transmits data to MSs 106B and106J, BS 104C transmits data to terminal 106C, and so on.

Increasing demand for wireless data transmission and the expansion ofservices available via wireless communication technology have led to thedevelopment of specific data services. As the amount of data transmittedand the number of transmissions increases, it becomes increasinglyimportant to utilize available bandwidth efficiently. Additionally,interference becomes a significant problem. Channel conditions mayaffect which transmissions may be sent efficiently. There is a need,therefore, for a method to hash mobile stations over multiple bandswhile avoiding unnecessary frequency changes. In the exemplaryembodiment, system 100 illustrated in FIG. 1 is consistent with aCDMA2000 wireless communication system.

FIG. 2 shows the states a mobile station passes through during callprocessing in a CDMA2000 wireless communication system. FIG. 2 shows anoverview of the call processing states, 200. Call processing begins whenthe MS powers up, 202. After power up, the MS enters the MobileInitialization state, 210. In the Mobile Station Initialization state,the mobile processes the Pilot and Sync Channels to acquire andsynchronize with the CDMA system. Upon entering the MobileInitialization state, the MS begins analog mode operations as part ofthe Initialization Task, 206. Once the Initialization Task 206 iscompleted analog mode operations end as the mobile has fully acquiredthe system timing. After acquiring the system timing, the mobile entersthe Idle State, 214.

While in the Idle State, the mobile monitors the Paging Channel or theForward Common Control Channel (F-CCH) to receive overhead andmobile-directed messages (such as a page message that indicates anincoming call) from the BS. Power control may also be performed whilethe MS is in the Idle State, 214. In addition, the MS monitors thebroadcast control channel (BCCH), performs registration, idle handoff,and position determination. These actions are necessary to assign afrequency band and frequency to the MS. The Paging Channel message mayrequire the mobile to respond with an acknowledgement (ACK) message ororiginate a call, or perform registration. If the MS is unable toreceive the paging channel the mobile may return to the MobileInitialization State, 210.

In the System Access State 222, the MS sends messages to the basestation BS on the Access Channel or Enhanced Access Channel. The BSlistens to these channels, and responds to the MS on either the PagingChannel or F-CCH. The MS receives an acknowledgement (ACK) to an AccessChannel transmission other than an Origination Message or a PageResponse Message.

In the Mobile Station Control on the Traffic Channel state, 230, the BSand MS communicate by using dedicated Forward and Reverse TrafficChannels, which carry user information, such as voice and data.

FIG. 3 is one example of a communication system supporting datatransmissions and adapted for scheduling transmissions to multipleusers. FIG. 3 illustrates the operation of the base stations 104 fromFIG. 1. FIG. 3 is detailed hereinbelow, wherein specifically, a basestation, 320 and base station controller (BSC) 310 interface with apacket network interface 306. Base station controller 310 includes achannel scheduler 312 for scheduling transmissions in system 200. Thechannel scheduler 312 determines which data is to be transmitted.

In addition, the channel scheduler 312 selects the particular data queuefor transmission. The associated quantity of data to be transmitted isthen retrieved from a data queue 330 and provided to the channel element326 for transmission to the remote station associated with the dataqueue 330. As discussed below, the channel scheduler 312 selects thequeue for providing the data, which is transmitted in a latertransmission.

Base station controller 310 may contain many selector elements 316,although only one is shown in FIG. 3 for simplicity. Each selectorelement 316 is assigned to control communication between one or morebase stations 320 and one mobile station (not shown). If selectorelement 316 has not been assigned to a given remote station, callcontrol processor 318 is informed of the need to page the remotestation. Call control processor 318 then directs base station 320 topage the remote station.

Data source 302 contains a quantity of data, which is to be transmittedto a given remote station. Data source 302 provides the data to packetnetwork interface 306. Packet network interface 306 receives the dataand routes the data to the selector element 316. Selector element 316then transmits the data to each BS 320 in communication with the targetMS remote station. In the exemplary embodiment, each base station 320maintains a data queue 330, which stores the data to be transmitted tothe MS.

The MS begins an initialization process when making a call. The MS firstdetermines the type of system timing by searching for usable pilotsignals. The pilot signal carries no information, but the MS can alignits own timing by correlating with the pilot signal. When thiscorrelation is found, the MS has synchronization with thesynchronization channel and can read the synchronization channel messageto refine its timing further. The MS may search for up to 15 seconds ona single CDMA channel before declaring failure and returning to systemdetermination to select another channel or another system. The searchingprocess is not standardized and the time needed to acquire the systemmay depend on the system implementation. In CDMA2000, there may be manypilot channels on a single CDMA channel. These pilots may includeorthogonal transmit diversity pilots, space time spreading pilots, andauxiliary pilots. During system acquisition, the mobile will not findany of these pilots because those pilots are on different Walsh codesand during the acquisition process the mobile is searching only forWalsh₀.

Once the mobile has synchronization, it reads the sync channel messageto further refine its timing. FIG. 4 shows the fields and field lengthsfound in the sync channel message. The synch channel message istransmitted continuously on the synchronization channel. This messageprovides the mobile with information to refine its timing and to readthe paging channel. Typically, only the LC_STATE and SYS_TIME fieldschange each time the sync channel message is transmitted.

The mobile receives information from the base station in the synchchannel message that allows it to determine whether it can communicatewith that base station. This information is found in the followingfields in the sync channel message:

-   -   MOB_P_REV—This field contains a value that is the maximum        protocol revision supported by the mobile. This value is stored        by the mobile.    -   P-REV—The maximum protocol revision supported by the base        station.    -   MIN_P_REV—The minimum protocol revision of a mobile that the        base station supports. If a mobile acquires a sync channel, and        MOB_P_REV<MIN_P_REV, it does not attempt to acquire service on        that system, but returns to system determination to try to        choose another system.    -   P_REV_IN_USE—A value computed by the mobile that is the protocol        revision currently being used by the mobile. Whenever the mobile        receives a sync channel message, it sets the value of        P_REV_IN_USE to the lesser of P_REV and MOB_P_REV. The mobile        will not request services or features that are not supported by        P_REV_IN_USE.

Once the mobile has completed system acquisition the mobile enters theidle state. The term idle state is something of a misnomer. The mobilecan be very busy in the idle state. In general, the mobile receives oneof the paging channels and processes the message on that channel.Overhead or configuration message are compared to the stored sequencenumbers to ensure that the mobile has the most current parameters.Mobile-directed messages are checked to determine the intendedsubscriber.

While in the idle state the mobile may perform the following functions:

-   -   perform paging channel monitoring;    -   perform registration procedures;    -   perform the response to overhead information operation (in        response to a system parameters message, neighbor list message,        CDMA channel list message or, access parameters message);    -   perform the mobile station page match operation;    -   perform the mobile station order and message processing        operation;    -   perform the mobile station origination operation;    -   perform the mobile station message transmission operation, if        directed by the user to transmit a message;    -   perform the mobile station power-down operation.

CDMA2000 uses four additional overhead messages: user zoneidentification message, private neighbor list message, extended globalservice redirection message, and the extended CDMA channel list message.

The user zone identification message and private neighbor list messageare used to support CDMA tiered services.

The extended global service redirection message redirects mobiles toanother system. The extended form of the message includes the ability toredirect a mobile as a function of its protocol revision.

The extended CDMA list message provides mobiles with the list of CDMAchannels used by the system. The extended form of the message includesinformation about the availability of quick paging channels, and whethertransmit diversity is supported on the available CDMA channels.

The base station may support multiple paging channels (Walsh functions)and/or multiple CDMA channels (frequencies). The mobile uses a hashfunction based on its international mobile subscriber identity (IMSI) todetermine which channel and frequency to monitor in the idle state. Thebase station uses the same hash function to determine which channel andfrequency to use when paging the mobile.

FIG. 5 shows the steps of the hashing function for the forward pagingchannel (F-PCH). The mobile always starts by using the primary pagingchannel, which is transmitted on Walsh channel 1. The system parametersmessage indicates whether there are multiple Walsh channels, and if so,the mobile uses the hash function to select a new one. The systemparameters message also indicates whether the CDMA2000 extended CDMAchannel list message is being sent on the F-PCH.

The method of hashing, 500 begins when the mobile acquires the syncchannel in step 502. In step 506 the mobile acquires the paging channel(Walsh 1). After acquiring the paging channel the mobile receives thesystem parameters message in step 510. Next, the mobile determines instep 514 if the system uses multiple paging channels. If the system doesuse multiple paging channels, a new paging channel Walsh code isselected in step 518. After selecting a new paging channel Walsh codethe mobile receives the system parameters message in step 522. If thesystem does not use multiple paging channels the next step in theprocess is to determine if the extended CDMA channel list has been sentin step 530. If the system does use multiple paging channels, afterselecting a new paging channel Walsh code in step 518 and receiving thesystem parameters message in step 522, the mobile proceeds to step 530to determine if the extended CDMA channel list has been sent. If theextended CDMA channel list message was sent it is received in step 534.If the mobile does not receive the extended CDMA channel list the mobilereceives the CDMA channel list message in step 526. If the mobilereceives the CDMA channel list message, the mobile determines whethermultiple CDMA channels are being sent in step 554. If so, the mobileuses the hash function to select a new frequency in step 560, tunes tothat frequency and starts over with acquiring and processing theoverhead messages. If only one channel is sent the mobile continues idlestate processing in step 564.

If the mobile receives the extended CDMA channel list message in step534, the mobile determines whether the base station and the mobilesupport the quick paging channel (QPCH) step 538 or radio configurationsgreater then 2, step 538. If so, the base station indicates in themessage which of the CDMA frequencies support those capabilities, andthe mobile selects from only those channels. Step 542 shows the step ofdetermining if the system supports multiple CDMA channels. If not themobile continues idle state processing in step 550. If so the mobileproceeds to select a channel in step 546 as described above.

Registration is the process by which a mobile makes its whereaboutsknown to the cellular system. Cellular systems use registration tobalance the load between the access channel and the paging channel. Thehashing method described above works in conjunction with registration toassign frequencies in accordance with the load balancing operations ofregistration. Without some type of registration, mobiles would have tobe paged over the entire cellular system, resulting in the need totransmit many pages per call delivery for a system with multiple basestations. A mobile would need to be paged as many times as there arebase stations in the system.

Requiring a mobile to register every time it moves to the coverage areaof a new base station increases the number of pages required. Due to thetransmission of the registration messages and their acknowledgements anoverwhelming load can be created on both the paging and access channels.

CDMA systems offer multiple ways to initiate registration. The differenttypes of registration may be enabled or disabled independently, whichallows cellular carriers to tailor any subset of registration methods tooptimize their systems. The registration methods chosen by a cellularcarrier are a function of parameters such as the cellular system size,expected mobility within the system, and call delivery statistics. Thebase station controls the types of registrations supported by fields inthe system parameters message, extended system parameters message, andANSI-41 system parameters message.

CDMA2000 supports ten registration methods. These methods are: power up,power down, timer based, distance based, zone based, ordered, implicit,traffic channel, parameter, and user zone based.

Non-autonomous registration is also performed in a CDMA2000 system. Thefollowing types of registration are considered non-autonomous:

-   -   Ordered registration—The mobile registers with the system after        the base station sends a registration order.    -   Traffic channel registration—The base station may obtain        registration about a mobile by sending a status request order on        the traffic channel, and receiving a status response message.        The base station may then notify the mobile that it is        registered by sending a mobile station registered message.    -   Parameter change registration—The mobile registers when certain        parameters that affect the process of delivering calls change in        the mobile. These parameters are the mobile station's station        class mark, preferred slot cycle, and mobile terminated call        indicator.    -   Implicit registration—Implicit registration occurs when the        mobile successfully sends an origination message or a page        response message. These messages convey sufficient information        to identify the mobile and its location.    -   User Zone based registration—The tiered services supported by        CDMA2000 may require that the mobile register when it enters a        user zone.

The registration method chosen by a cellular carrier is a function ofparameters such as the cellular system size, the expected mobilitywithin the system, and call delivery statistics. Since systems may varysubstantially with respect to these measures, CDMA specifications offerthe multiple registration methods described above. The differentregistration procedures can be enabled or disabled independentlyallowing a cellular carrier to optimize the use of their system.

Registration is carried out with a registration message. FIG. 6 showsthe structure of a registration message. The REG TYPE field is used toindicate timer-based, power up, zone-based, power down, parameterchange, and ordered or distance based registration.

Registration may be one of two types: autonomous and non-autonomous. Inan autonomous registration the mobile station initiates the registrationin response to an event, without being explicitly directed to registerby the base station controller. There are six forms of autonomousregistrations, which are discussed below:

-   -   Power-up registration—The mobile registers when it powers on,        switches from using the alternate serving system, or switches        from using the analog system.    -   Power-down registration—The mobile registers when it powers off        if previously registered in the current serving system.    -   Timer-based registration—The mobile registers when a timer        expires.    -   Distance-based registration—The mobile registers when the        distance between the current serving cell and the serving cell        in which it last registers exceeds a threshold.    -   Zone-based registration—The mobile registers when it enters a        new zone.

The various forms of autonomous registration can be globally enabled ordisabled by the base station controller. The forms of registration thatare enabled and the corresponding registration parameters arecommunicated in an overhead message transmitted on the CDMA pagingchannels.

Non-autonomous registration method include: ordered, traffic channel,parameter change, and implicit. All non-autonomous registration methodsprovide the ability to update the home location register (HLR)/visitorlocation register (VLR) when responding to orders on the paging channel,or using the access channel or traffic channel.

The cellular system may become aware of a mobile within its coveragearea for which it does not possess all the information required todeliver a call (e.g., following receipt of an origination message fromthe mobile). In this case the cellular system can order the mobile toregister using the request order.

FIG. 7 shows the structure of the request order and the fields containedin the order. The mobile responds to the request order with aregistration message on the access channel and updates its datastructures as for any other registration.

Another non-autonomous registration is traffic channel registration.Traffic channel registration refers to a method in which the mobilereceives registration related information while on the traffic channel.Since the information exchange on the traffic channel causes lessinterference to other users than exchanges occurring on the paging andaccess channels, the CDMA system may provide for transmission ofregistration information on the traffic channel, preventing manyinstances of automatic registration following a call. One example wheresuch registrations may occur is calls involving intersystem handoffs.

Provision of registration information to a mobile can be done followingthe reception of a release order from the mobile and prior totransmission of a release order to the mobile. At this stage,information exchanges between the base station and the mobile have noeffect on voice quality.

FIG. 8 shows the structure of the parameter change registration. Certainparameters in the mobile may directly affect the process of deliveringcalls to the mobile and therefore should be updated in the systemwhenever a change in them occurs. These parameters are the mobilestation's Station Class Mark (SCM), preferred slot cycle, andmobile-terminated call indicator.

The SCM can change in mobiles that can be attached to a vehicle and thendetached and used as a portable phone. Since under these differentcircumstances the mobile would transmit different power and havedifferent reception capabilities, the base station should be made awareof the change so it can use the information in its call deliveryalgorithm.

The preferred slot cycle index refers to a capability of certain CDMAphones to monitor the paging channel only in selected time slots, thusreducing processing load and increasing battery life. A base stationthat attempts to page a mobile station must be aware of the slot cyclebeing used by the mobile so that it transmits the pages in those slotsin which the mobile station monitors the paging channel.

Finally, the mobile station maintains a call termination indicator. ACDMA phone may be programmed independently to accept calls when in thecoverage area of a base station belonging to the system from whichservice is provided (the “home” system), when roaming in the servingsystem but a different network (a Network Identification “NID” roamer”),or when roaming in a different system (a Systems Identification “SID”roamer).

The call termination indicator is therefore a function of the mobilestation's roaming status and the call termination preference programmedfor that roaming status. If the call termination indicator changes,either due to a change in roaming status or to a change in preference),the base station should be notified so it can determine if pages shouldbe transmitted to the mobile station.

Implicit registration occurs when the mobile station and base stationexchange messages that are not directly related to registration butconvey sufficient information to identify the mobile and its location(to within a base station coverage area) to the cellular system.

For compatibility with other registration schemes used in other wirelesscommunication systems, the mobile station considers that it hasimplicitly registered only after a successful transmission of anorigination message or a page response message.

During routine operation, the mobile station can provide status updatesto the system in origination messages and page response messages. Thiscapability reduces the number of registration messages that are needed.

FIG. 9 shows the fields required in the origination message. Theorigination message, sent by the mobile station, contains enoughinformation to implicitly register the MS.

A number of issues are will known regarding paging of mobiles that areoperating near system boundaries. Among these issues is thedetermination of the proper base station controller (BSC) for paging amobile station that moves from one system to another. Autonomousregistration after each change of system helps, but cannot completelyresolve this problem. Since registration cannot be instantaneous, thereis always some period during which the Home Location Register (HLR) isunaware that the mobile station has changed serving systems.

If autonomous registration occurs each time a mobile station enters acell in a new serving system, another issue arises: mobile stations thatregister upon each change of serving system could issue an excessivenumber of registration requests when moving along a system boundary.This is because propagation effects can cause the optimum serving systemfrom the mobile station's viewpoint to change rapidly while the mobilestation is in motion.

The mobile station maintains a list of Systems Identification numbers(SID) and Network Identification numbers (NID) in which it registered,the SID_NID_LIST. When the mobile station registers in a given (SID/NID)pair, it add the pair to the list and starts a timer for the paircorresponding to the SID and NID in which it previously registered. Ifthe mobile station returns to the coverage area of a base station thatbelongs to a (SID/NID) pair on its list, it does not re-register. Once atimer expires, the mobile station deletes the pair associated with thetimer from the list. If the mobile station happens to be in the coveragearea of a base station belonging to the (SID/NID) whose timer expired,it re-registers, adding the pair back to the list without a timer.

The BS can control storage of multiple SIDs and/or NIDs in the mobilestation's SID_NID_LIST through the use of the MULT_SIDS and MULT_NIDSparameters sent in the system parameters message.

FIG. 10 shows the fields and fields lengths of the system parametersmessage. When MULT_SIDS is set to zero, the mobile station will notstore multiple entries having identical SIDs. Thus, when it registers aparticular (SID, NID) pair, it removes from the list another pair havinga different SID if such exists. Similarly, when MULT_NIDS is set tozero, the mobile station stores only one (SID, NID) pair for every NIDin which it registers.

The system parameters message control which types of registration are tobe used in the system. From this overhead message the mobile station candetermine which types are to be used, and the values of operation.

The REG_ZONE field is set to the registration zone of the base station.The TOTAL_ZONES field is set to the number of registration zones themobile station is to retain for the purposes of zone-based registration.The ZONE_TIMER sets the length of the zone registration timer to be usedby the mobile station. The ZONE_TIMER ranges from 1 to 60 minutes.

A key part of the registration process is assigning the mobile stationan operating frequency. This frequency assignment also has implicationsfor the system as a whole. Mobile stations should be distributed acrossmultiple frequencies and bands so that interference is minimized andsystem operating parameters maintained in their optimum ranges. Thegoals of the registration process include distributing idle mobilestations between frequency bands, minimizing implementation time forchanges to the registration process, minimizing message exchanges,especially registrations on band changes, avoiding mobile stationredirection and re-assignment, and avoiding the use of a second pagingchannel, which adversely affects power usage and requires a second Walshcode.

Modifying the hashing process would lead to improved system performance.System performance could be enhanced if hashing could be alternativelyenabled and disabled across frequency bands. Further system performanceimprovements would be possible if hashing weights could also be enabledand disabled across frequency bands. In the case of frequency bandoverlay, hysteresis could be provided for cross-band registrations withthe use of overlay paging zones to reach those mobiles in the overlyingfrequency bands. Embodiments of the present invention offer the abovehashing features.

The enhancements discussed above may be implemented with changes to thehashing process. One embodiment would allow different registrationperiods for different classes of mobile stations. This would allow thenetwork to divide the mobile stations into classes such as regular andlimited mobility. For the mobile stations with limited mobility, thatis, those moving slowly or not at all through the system, may have alonger registration period.

An embodiment of the present invention would provide an improvedmechanism to distribute mobile stations over frequency bands byutilizing inter-band hashing using the Extended CDMA Channel ListMessage (ECCLM).

A further embodiment would allow a band or subclass query of the networkusing the overhead channels. This may be a solution to the problem offrequent registrations due to a change of frequency band by the mobilestation.

An embodiment of the invention provides enhancements to the ECCLM toallow improved hashing. The modifications allow MOB_P_REV based hashing.This would allow hashing based on the mobile station's maximum protocolrevision.

A further embodiment would allow a non-uniform distribution of mobilesacross frequencies through weight-based hashing. This may beaccomplished by adding a new parameter to the ECCLM, frequency weight,for each frequency to indicate the weight associated with thatfrequency. These frequency weights are taken into account when hashing,that is, a larger weight assigned to a frequency results in more mobilestations hashed to that frequency.

A still further embodiment would allow inter-band hashing. This may beaccomplished by adding a frequency band class and a frequency bandsubclass parameter to each listed frequency. These goals are achieved byadding band information to legacy frequencies in the legacy part of theECCLM. Legacy frequencies are those utilized by existing IS-95 systems.

A mobile station may hash to a frequency on a different band subclass ordifferent band class. The sub-band information allows a two levelhashing process. Two level hashing reduces the number of band changeswhen the mobile station is in the idle state. In this embodiment themobile station goes directly to the idle state. This action reduces thenumber of hops to the idle state in the new band or new frequency. Thisaction is intended to be used in cases where the coverage of thedifferent frequency bands is similar.

FIG. 11 shows weight-based hashing coupled with a two-level hashinglogic 1/2 as described in the above paragraphs.

The above enhancements allow the mobile station to avoid registration ifthe ECCLM resulted in a frequency band change. This results in lessdrain on system resources since the mobile station avoids wastingbattery power on receiving paging and redirection messages. In addition,drain on system resources is reduced, since the system needs to sendfewer messages in order to hash mobile stations to frequencies.

The two level hashing reduces the occurrence of band changes by themobile station when the mobile station performs and idle handoff,processes the new ECCLM, and ends up in the same band it was previouslyusing. In addition two-level hashing isolates hashing within a frequencyband while still allowing for a frequency band re-hash if needed.

FIG. 12 illustrates the steps of the two-level hashing of an embodimentof the invention. The process, 1200, begins when the mobile stationreviews the channels contained in the ECCLM and eliminates thosechannels it does not support, and sorts the bands and frequencies inorder to provide stable hashing across base stations. In the past,mobile stations were required to support all channels. Since theintroduction of new band classes that extend well beyond the currentbands, this support cannot be guaranteed in the future. After reviewingthe list of channels in the ECCLM, in step 1206, the MS hashes into aband, taking the aggregate weight assigned to the channels in that bandinto account. In step 1210 the MS eliminates channels in the ECCLM thatare outside of the chosen frequency band. In step 1214 the MS hashesinto a channel within the chosen frequency band, taking into account theassigned weights.

Inter-band hashing presents a potential problem that needs to beaddressed. The MS may not support all the frequency bands or frequencyband subclasses included in the ECCLM. The MS needs to skip over thesefrequency bands or frequency band subclasses to select a frequency.Sorting provides a mechanism to remove unsupported subclasses. However,the base station needs to know which frequency bands or frequency bandsubclasses the MS supports. In the overhead messages the base stationsignals which frequency bands and frequency band subclasses are deployedin that sector. In each registration, the MS indicates which ones on thebase station list the MS supports. The network may also query as to thefrequency band and frequency band subclasses that are supported. Thisinformation is received via a status request which is received by theMobile Switching Center (MSC). The MSC passes that information down toeach Base Station Controller (BSC) when sending a message to the MS.Even with inter-band hashing the MS must perform a power up registrationwhenever it changes frequency bands or frequency band subclasses.

FIG. 13 illustrates two-level hashing with assigned weights. The ECCLMof band class 2 is transmitted to at least one mobile station. Themobile station sorts the third CDMA channel list and discardsfrequencies, such as frequency 3 in subclass 1, that are not supported.A two level hashing process, as described above, is then performed.Sorting bands and frequencies provides for stable hashing across basestations.

An additional embodiment would provide for the base station to signal inthe overhead messages the frequency band or frequency band subclass ofinterest. The MS would indicate its capabilities during registration.

A further embodiment provides for the MS to indicate any change ofhardware capability with one bit in the registration process. The MSCqueries the MS for capabilities and uses this information for subsequentpaging messages. The one bit added to the registration signals a mobileequipment change. This triggers the network to ask the MS about the newor different hardware capabilities.

Thus, a novel and improved method and apparatus for schedulingtransmissions in a communications system has been described. Those ofskill in the art would understand that the data, instructions, commands,information, signals, bits, symbols, and chips that may be referencedthroughout the above description are advantageously represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof. Those of skillwould further appreciate that the various illustrative logical blocks,modules, circuits, and algorithm steps described in connection with theembodiments disclosed herein may be implemented as electronic hardware,computer software, or combinations of both. The various illustrativecomponents, blocks, modules, circuits, and steps have been describedgenerally in terms of their functionality. Whether the functionality isimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.Skilled artisans recognize the interchangeability of hardware andsoftware under these circumstances, and how best to implement thedescribed functionality for each particular application. As examples,the various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented or performed with a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components such as,e.g., registers and FIFO, a processor executing a set of firmwareinstructions, any conventional programmable software module and aprocessor, or any combination thereof designed to perform the functionsdescribed herein. The processor may advantageously be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, programmable logic device, array of logicelements, or state machine. The software module could reside in RAMmemory, flash memory, ROM memory, EPROM memory, EEPROM memory,registers, hard disk, a removable disk, a CD-ROM, or any other form ofstorage medium known in the art. An exemplary processor isadvantageously coupled to the storage medium so as to read informationfrom, and write information to, the storage medium. In the alternative,the storage medium may be integral to the processor. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in atelephone or other user terminal. In the alternative, the processor andthe storage medium may reside in a telephone or other user terminal. Theprocessor may be implemented as a combination of a DSP and amicroprocessor, or as two microprocessors in conjunction with a DSPcore, etc.

In further embodiments, those skilled in the art will appreciate thatthe foregoing methods can be implemented by the execution of a programembodied on a computer readable medium, such are the memory of acomputer platform. The instructions can reside in various types ofsignal-bearing or data storage primary, secondary, or tertiary media.The media may comprise, for example, RAM accessible by, or residingwithin, the client device and/or server. Whether contained in RAM, adiskette, or other secondary storage media, the instructions may bestored on a variety of machine-readable data storage media, such as DASDstorage (e.g., a conventional “hard drive” or a RAID array), magnetictape, electronic read-only memory (e.g., ROM or EEPROM), flash memorycars, an optical storage device (e.g., CD-ROM, WORM, DVD, digitaloptical tape), paper “punch” cards, or other suitable data storage mediaincluding digital and analog transmission media.

While the foregoing disclosure shows illustrative embodiments of theinvention, it should be noted that various changes and modificationscould be made herein without departing from the scope of the inventionas defined by the appended claims. The activities or steps of the methodclaims in accordance with the embodiments of the invention describedherein need not be performed in any particular order. Furthermore,although elements of the invention may be described or claimed in thesingular, the plural is contemplated unless limitation to the singularis explicitly stated.

Preferred embodiments of the present invention have thus been shown anddescribed. It would be apparent to one of ordinary skill in the art,however, that numerous alterations may be made to the embodiments hereindisclosed without departing from the spirit or scope of the invention.Therefore, the present invention is not to be limited except inaccordance with the following claims.

1. A method comprising: hashing a mobile station to a frequency band;and hashing the mobile station to a specific frequency within thefrequency band.
 2. The method of claim 1, further comprising: allowing adifferent length registration period for different classes of mobilestations.
 3. The method of claim 2, further comprising: placing mobilestations into classes, wherein the classes comprise regular and limitedmobility classes; and allowing a longer registration period for mobilestations in the limited mobility class.
 4. A method comprising: hashinga mobile station to a frequency band using inter-band hashing, whereinthe inter-band hashing is based on a message.
 5. The method of claim 4,further comprising: wherein the message includes a list of frequencies.6. A method comprising: sending a message from a first device to asecond device; receiving information in the message at the first device;hashing the first device to a frequency band based on the information inthe message.
 7. The method of claim 6, further comprising: wherein themessage contains information about protocol revisions supported by thefirst device.
 8. A method comprising: assigning a weight to eachfrequency within a frequency band; hashing a mobile station to afrequency based on the weight assigned to the frequency; anddistributing mobile stations across frequencies based on the weightsassigned to the frequencies, resulting in a non-uniform distribution ofmobile stations across the frequencies within the frequency band.
 9. Themethod of claim 8, further comprising: sending a message to the mobilestation containing a list of frequencies, wherein each frequency isassigned a frequency weight.
 10. A method comprising: assigning a weightto each frequency within more than one frequency band, sending a messageto a mobile station containing a list of frequency bands and a list offrequencies within those frequency bands with assigned frequencyweights; reviewing by the mobile station of the frequency bands andfrequencies contained within the message; eliminating the frequenciesnot supported by the mobile station; sorting of the bands andfrequencies; hashing a mobile station to a frequency band; and hashing amobile station to a frequency within the frequency band based on theassigned frequency weights.
 11. The method of claim 10, furthercomprising: signaling the mobile station the frequency band of interest.12. The method of claim 11, further comprising: signaling the mobilestation the frequency of interest.
 13. The method of claim 10, furthercomprising: querying the mobile station to indicate any change ofhardware capability during registration.
 14. A computer-readable mediumincluding computer-executable instructions, comprising: hashing a mobilestation to a frequency band; and hashing the mobile station to aspecific frequency within the frequency band.
 15. The program as inclaim 14, further comprising: allowing a different length registrationperiod for different classes of mobile stations.
 16. The computerprogram of claim 15, further comprising: instructions for placing mobilestations into classes, wherein the classes comprise regular and limitedmobility classes; and allowing a longer registration period for mobilestations in the limited mobility class.
 17. A computer programcomprising computer-executable instructions for: hashing a mobilestation to a frequency band using inter-band hashing, wherein theinter-band hashing is based on a message.
 18. The computer program ofclaim 17, further comprising: wherein the message includes a list offrequencies.
 19. A computer program comprising computer-executableinstructions for: sending a message from a first device to a seconddevice; receiving information in the message at the first device;hashing to first device to a frequency band based on the information inthe message.
 20. The computer program of claim 19, further comprising:wherein the message contains information about protocol revisionssupported by the first device.
 21. A computer program comprisingcomputer executable instructions for: assigning a weight to eachfrequency within a frequency band; hashing a mobile station to afrequency based on the weight assigned to the frequency; anddistributing mobile stations across frequencies based on the weightsassigned to the frequencies, resulting in a non-uniform distribution ofmobile stations across the frequencies within the frequency band. 22.The computer program of claim 21, further comprising instructions for:sending a message to the mobile station containing a list offrequencies, wherein each frequency is assigned a frequency weight. 23.A computer program comprising computer-executable instructions for:assigning a weight to each frequency within more than one frequencyband, sending a message to a mobile station containing a list offrequency bands and a list of frequencies within those frequency bandswith assigned frequency weights; reviewing by the mobile station of thefrequency bands and frequencies contained within the message;eliminating the frequencies not supported by the mobile station; sortingthe bands and frequencies; hashing a mobile station to a frequency bandwhere a weight of a frequency band is an aggregate of weights assignedto frequencies in the band; and hashing a mobile station to a frequencywithin the frequency band based on the assigned frequency weights. 24.The computer program of claim 23, further comprising instructions for:signaling the mobile station the frequency band of interest.
 25. Thecomputer program of claim 24, further comprising instructions for:signaling the mobile station the frequency of interest.
 26. The computerprogram of claim 23, further comprising instructions for: querying themobile station to indicate any change of hardware capability duringregistration.
 27. In a wireless communication system, a network,comprising: means for hashing a mobile station to a frequency band;means for determining frequency band assignments for each mobilestation; means for hashing the mobile station to a specific frequencywithin the frequency band; and means for repeating the hashing processfor each mobile station within the network.
 28. An apparatus in awireless communication system, comprising: means for hashing a mobilestation to a frequency band; and means hashing the mobile station to aspecific frequency within the frequency band.
 29. An apparatus in awireless communication system, comprising: means for hashing a mobilestation to a frequency band using inter-band hashing, wherein theinter-band hashing is based on a message.
 30. An apparatus in a wirelesscommunication system, comprising: means for assigning a weight to eachfrequency within more than one frequency band, means for sending amessage to a mobile station containing a list of frequency bands and alist of frequencies within those frequency bands with assigned frequencyweights; means for reviewing by the mobile station of the frequencybands and frequencies contained within the message; means foreliminating the frequencies not supported by the mobile station; meansfor hashing a mobile station to a frequency band; and means for hashinga mobile station to a frequency within the frequency and based on theassigned frequency weights.